1 Field of the Invention
This invention relates to an image recording and displaying apparatus which utilizes an array of aligned light sources such as a semiconductor laser array.
2 Description of the Prior Art
There are known image recording and displaying apparatuses having a single source of light. FIG. 1 shows an example of such apparatuses wherein a divergent beam emitted from a semiconductor laser 1 is collimated by means of a collimator lens 2 and falls on a rotary multifaceted mirror 3. The beam which has been reflected and deflected by the rotary multifaceted mirror is then brought to a focus on a surface 5 to be scanned through an imaging lens 4 such as an f.sub..theta. lens or the like. By modulating the semiconductor laser, the desired image can be formed on the surface to be scanned.
If an array of aligned light sources are used in such an apparatus, various advantages will be obtained. The term "an array of aligned light sources" is defined herein as such a construction that a plurality of semiconductor lasers 1a, 1b and 1c which can be independently driven and modulated are brought into a line as shown in FIG. 2. If these light sources are used instead of a single light source, one can obtain the following advantages:
1. The apparatus can be run at higher speed because a plurality of scanning lines are utilized for recording and displaying. PA1 2. For this reason, a rotary multifaceted mirror, a galvano mirror and the like can be operated at lower speed. PA1 3. Semiconductor lasers can be used with lower power resulting in prolonged life. PA1 However, if such light sources are used in the prior art optical systems without modifying, there can be provided such disadvantages as described hereinbelow. PA1 FIG. 3 illustrates an example of an optical system wherein three semiconductor lasers 1a, 1b and 1c are used as a light source portion 1. Beams emitted from the semiconductor lasers 1a, 1b and 1c are oscillated to distribute with maximum intensity in a direction perpendicular to the end face of the light source portion 1. When the beams are collimated by a collimator lens 2, the beam from the semiconductor laser 1b on the optical axis only becomes parallel to the axis while the remaining beams from the semiconductor lasers 1a and 1c located off of the axis are collimated to intersect the optical axis with a finite angle .theta.. This angle .theta. is obtained by the use of the following formula: EQU .theta.=n 1/f (rad)
where f is a focal length in the collimator lens, 1 is a pitch in the light source array and n is the number of light sources. It is considered that the pitch 1 in the semiconductor laser array must be about 0.1 mm minimum because of various problems accompanied by heat emanation, manufacturing techniques and the like. Now, if the focal length f of the collimating lens is 10 mm, and the number of lasers n is 8, the angle .theta. is EQU 8.times.0.1/10=0.08 rad.=4.6.degree..
Further, if the distance d between the focal plane 6 of the collimator lens and the multifaceted mirror is 100 mm, a light spread .DELTA. on the reflecting surface on the multifaceted mirror is EQU .DELTA.=d.multidot..theta.=100.times.0.08 =8 mm.
This value cannot be neglected. As a result, if light sources 1a, 1b, 1c and 1d are disposed along such a line that is parallel or substantially parallel to the primary scanning direction as shown in FIG. 4A, light spots would be spread on the reflecting surface 3a of the multifaceted mirror 3 in the rotational direction thereof as shown in FIG. 5. Consequently, each of the beams 7a, 7b and 7c collimated by the lens 2 will have a quantity of reflected light per rotational angle .theta. of the multifaceted mirror 3 which is distributed as shown in FIG. 6. As seen from FIG. 6, the range of rotational angle 2.theta..sub.o in which the scanning can be effectively made is extremely narrow in comparison with the case of a single source of light.
In order to overcome such a problem, the multifaceted mirror must be increased in diameter. This means that the multifaceted mirror cannot be easily driven or otherwise a motor for driving this mirror should have higher power resulting in increased cost and size.
If the light sources 1a, 1b, 1c and 1d are located along such a line that is perpendicular to the primary scanning direction as shown in FIG. 4B, the multifaceted mirror may have the same diameter as in a single light source. However, it must be increased in thickness since the beam spread on the reflecting surface is widened to distribute along the rotational axis of the multifaceted mirror. Similarly, such an arrangement will have the same problems as in the multifaceted mirror having its increased diameter.